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The vertical resolution varies with geometric height.  The vertical resolution is greatest (most fine) in the planetary boundary layer while more coarse near the model top.  The “σ-levels” follow the earth’s surface in the lower layers of the troposphere, where the Earth’s orography has large variations, but in the upper stratosphere and lower mesosphere they are surfaces of constant pressure.  There is a smooth transition from “σ-levels” to pressure levels between lower and upper levels.

• The IFS ENS and Extended Range ENS models have 137 levels in the vertical; the four lowest levels are at 10m, 31m, 54m, 79m above the model surface.
• The IFS Seasonal model has 91 levels in the vertical; the four lowest levels are at 10m, 34m ,68m, 112m above the model surface.

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(Note: In older material there may be references to issues that have subsequently been addressed)

• View information on resolution of current ECMWF models.
• View further information on current IFS resolution.
• Read more on the Octahedral Reduced Gaussian Grid.
• Read more on Operational Configurations

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